Various sanders have been disclosed in prior art publications which have a pivotally oscillating output shaft, namely, U.S. Pat. No. 4,920,702 (Klaus et al) and published PCT patent application No. PCT/US93/07589 (Everts et al) (FIG. 16 embodiment) which is incorporated by reference herein. These sanders employ generally triangular heads which are centrally mounted on the center line of the pivotally oscillating output shaft. The central orientation of the driveshaft axis relative to the triangular sanding pad results in a balanced movement. However, the sanding pad does not extend very far beyond the front of the housing, limiting the use of the tool in tight places. In order to located the pad forward of the housing, sanding pads have been located on the ends of centrally pivoted levers as shown in U.S. Pat. No. 2,350,098 (Decker) as well as in FIGS. 2-3 of the previously cited Everts et al PCT application, which is commercially known as the Ryobi DS1000 sander.
The present invention is incorporated in a sander having a pivotally oscillating output shaft. However, the sanding head is located completely forward of the pivot axis. This design enables the driveshaft to be supported on a pair of spaced apart bearings, while having the sanding pad located forward of the tool body so that it can reach into tight places.
A problem originally faced when designing the present invention was that the sanding head vibrated, affecting sanding performance and causing unwanted noise. The sanding head, when viewed with a strobe light, cyclically wobbled out of plane, much the same way a coin spinning on edge wobbles as it slows to a stop.